The beneficial reuse of waste materials has long been a priority in the protection of human health and the environment. More recently, attempts have been made to use a larger variety of waste as a manufacturing feedstock, primarily through the use of various gasification techniques.
In the United States, the use of gasification technologies for waste disposal has been attempted with varying degrees of success since the 1970s. One of the biggest barriers to the use of waste materials as a manufacturing feedstock is the diversity of the chemical composition, moisture content, and physical characteristics of waste materials. This diversity is compounded by the variations in waste material from location to location, as well as changes in the characteristics of waste over time. Unlike fossil-based feedstocks (e.g., natural gas, coal) that have fairly consistent chemical composition and physical characteristics from one location to the next, waste materials are inherently diverse making the quality of waste-derived products more difficult to achieve.
The most common methods used to overcome the problems of waste diversity involve sorting; separating; mixing; or a combination of the three. Sorting and separating provides value in identifying wastes that have high energy value and desirable chemical compositions, but they are both capital and energy intensive, rendering the systems cost prohibitive. Mixing waste provides a less expensive method for homogenizing the waste from one batch to another, but the potential for undesirable chemical reactions increases risks to human health and the environment.
Synthesis gas (syngas) derived products, with integrated electric power co-generation using virgin fossil feedstocks and/or waste feedstocks, have been manufactured on an industrial scale since the mid-20th Century. It is a well understood practice that essentially involves the recycling of Carbon, Hydrogen and Oxygen at the molecular level and managing energy efficiencies in order to optimize the financial results for the systems' owners. Historically, this has meant that a portion of the syngas is combusted in an integrated gasification combined cycle (IGCC) system to increase net power production, at the expense of stack emissions. Given the current realities of the national energy security situation, there is an ever increasing demand for syngas-derived products made from domestic and renewable resources. However, there is opposing pressure from environmental protection priorities to reduce combustion stack emissions and greenhouse gas emissions.
The problem with conventional approaches is the persistence of an open-loop in the mass and energy balancing of the whole system. Zero-emissions can be achieved using conventional systems, but normally require an energy input in the form of pure Oxygen, natural gas (methane) or grid power. Even though this can theoretically be solved using 100% renewable energy, the financial sustainability of the system becomes questionable due to the cost of utilities.